Abstract：In order to investigate the evolution process of internal flow in residual heat removal pumps during different starting periods, the transient flow field in a residual heat removal pump is simulated by using a method based on the combination of Flowmaster and CFD technology, and the evolution processes of pressure, velocity and vortex in the impeller and guide vanes are analysed. A mathematical model is built for the motor starting period with Matlab-Simulink, then the motor speed variation with time is obtained through a simulation, showing the rated speed can be achieved at 5.5s. Further, a model is generated in Flowmaster to simulate the starting process of the residual heat removal pump, and the flow variations with time are obtained during different starting periods. Finally, the internal flow fields in the pump are analysed in ANSYS CFX during different starting periods. It is shown that the pressure gradient is obviously sharper during the alternating starting period than during the minimum flow starting period in pipeline because the pump is subject to a high temperature and high pressure condition in the former period, while the pressure distribution in the volute almost remains unchanged in the dual-pump operating period. The vortex evolution processes in the impeller and guide vanes all experience three different stages, namely, vortex generation, separation and disappearance in three different starting periods. Note that the vortex disappears sooner during the dual-pump operating period than in the other two periods. The flow in the flow passages becomes uniform at 5.5s, reflecting the inertia action of fluid affects the development of flow field in different starting periods significantly. The head is the minimum during the dual-pump operating period in comparison with the other periods, and the head rises with increasing impeller rotating speed with an overshoot as the speed stops accelerating. The overshoot effect is mostly evident during the dual-pump operating period.
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